MA1N LI Y3.6m telescopeMAINTENANCE MANUALNUMBER 8

ALIGNMENT FACILITIES

Edition may 1977 D.Plathner

3.6m telescopeMAINTENANCE MANUALNUMBER 8

ALIGNMENT FACILITIES

Edition may 1977 D.Plathner

CONTENT P~E

1. Introduction 12. General alignment information 1

2.1. Sighting instrument generalities 12.2. Auto-collimation 12.3. Collimation 22.4. Auto-reflection 32.5. Setting of targets and mirrors 3

3. Technical details of alignment facilities 43.1. Sighting telescope 43.2. EQuipment for sighting telescope 73.3. One-second theodolite 133.4. EQuipment for theodolite 153.5. Targets + target holders 17

4. Alignment procedures 204.1. Instrument pole 204.2. Perpendicularity of alpha and delta axis 214.3. Perpendicularity of delta and tube axis 234.4. Mirrors and top units 24

5. Maintenance instructions 266. Annex 29

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1. Introduction

This manual mainly gives operation instructions and des­criptions of the alignment facilities and instrumentsavailable tor the 3.6 m telescope.

In the second part alignment procedures are indicatedwhich are necessary to bring the telescope into properposition for its optical performance.

As most of the alignment eQuipment asks for shop adjust­ment at the deliverer's due to their high Quality opticalperformance maintenance informat~on is limited to lampexchanges and level adjustments.

2. General alignment informations

In this chapter details are given which are of interestfor the general alignment practice.

2.1.

2.2.

The 0ltical ali~ment instruments which will bedescr bed in th1s manual have:

upright imagesmetric scales3600 readingsno co••on voltage for the illumination facilitiesautocollimation eQuipment.

Auto-collimation is the most precise optical methodto cheek the sQuareness of a mirror to the line ofsight.

The sighting instrument (theodolite or alignmenttelescope) is focused at infinity. The rays of :.light are, therefore, collimated (parallel) and canbe reflected back along their own path forming an

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REFLECTEDIMAGE

image of the crosslines inthe plane of the installedcrosslines themselves.

If the mirror is tilted,the image of the crosslinesis displaced (fig. 2.1.)

The method can only be usedto check sQuareness, notto measure tilt.

Fig. 2.1. Auto-col­limation image

2.;.

If measurements are neces­sary one has to install acollima~or in the line ofsight instead of a mirr~r.

The collimator is a device for projecting paral­lel rays of light, Basically it consists of acollimating lens, a lens set at tb~ ~oCAl nla-ne of the lens and means for illuminating thetarget. When the collimator is viewed by ~ne

si~hting instrument an image of the tilt target(fig. 2.2) is seen when the instrument is focusedat infinity, irrespective of the actual distance,Also the size of the image is constant, but in­tensity and constrast change.

When the axis of the Sigbt~g

instrument is parallel to theaxis of the collimator, thetarget is seen centered on thecrosslines, even if the axis ofthe two instruments are not alig­ned. If the collimator is tiltedhowever, the target appears off- .center and the tilt can directly U~read in minutes of arc.

Fig. 2.2Tilt target

A second varget called displacement target (fig.2.;.) is printed on the cover glass and is used

for measuring displacementof the collimator axis fromthe sighting instrument axis.The instrument is then focusedon that target, so one does notinterfere with the others, pro­vided that the distance is lessthan 20 meters.

Fig. 2.;. Displa­cement target

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2.4. The faster but less accurate method of auto-reflec­tion can be used by instruments eQuipped with lateralmicrometric displacement possibilities and an il­luminated target (fig. 2.4.) on the cove~ "lass oftbe instrument. When tbe mirror is tilted witbrespect to tbe instrument line of sight, tbe ima-

ge of the target appearsto be offset from the cross­lines. The figures on the

target indicate gradient inmillimetres per meter when

\ tbe mirror is placed one() meter from tbe sigbting ins­

trument.

The gradients at tbe mirror­to-instrument distances areproportional.

Gradient- circle value/distan­ce instrument mirror.

Fig. 2.4. Cove r glassTarget

A conversion table for gradients expressed in arc secondsis given in table I of tbe annex.

2.5. To set targets or mirrors on tbe axis of the 3.6 mtelescope is extremely difficult due to tbe big dia­meters and mainly due to tbe limited possible anglesof rotation.

A metbod has, tberefore, been developed wbicb permitsto set targets and mirror asking for a rotation through90 degrees.

This metbod is, bowever, only valid under tbe assum­tion tbat for a certain rotation tbere will onlyexist one axis, i.e. excentricity effects are zero.

One sets a target in tbe estimated center of rotationand aligns a sigbting instrument witb micrometerreading to tbe target. Tbe instrument is mountedto tbe stationary part and tbus does not rotate witbthe target.

After a rotation through 90 degrees onereads the position of the target with the sight­ing instrument'and plots the displacements intoan x-y coordinate system (see fig. 2.5.).

The intersection of the mid-perpendicular witbtbe circle over the connecting line between thetwo points is the center of rotation.

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yCmrn.J

[mm J

Center of rotation

Flg.2.5

Tbe decision between tbe two possibilities isgiven by the direction of rotation.

Although one measurement should theoreticallybe enough it is in practice necessary to repeatit two or three times to eliminate reading er­rors and increase accuracy.

The same method can be applied for setting mir­rors sQuare to the line of sight by working inauto-reflection. As the distance is in this casehowever, dobbled tbe measured values have to bedivided by two before plotting.

3. Technical det~gnment faoiliiies

After baving given some information on the techniQuesto be used for the alignment of the 3.6 m telescopethe following chapters will give details about theinstrument facilities available.

3.1. ~ting tglesoope

Tbe simplified general arrangement of the sight­ing telescope is illustrated in the frontispie­ce (fig. 3.1.). The ob~ective lens is tbe mainligbt-gathering component of the optical system.This, together with the focusing lens, producesan inverted real ima~e somewhere in the area thatinoludes tbe plane of the crosslines. Movementof the focusing lens allows tbe image to be brougbtacourately, into the plane of the crosslines -which is the correct working condition.

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Eyepiece

E,,"or I'ns {

Fo',"sing lens {

Objective lens fl

Micrometer block {

Cover glass {

Fig. 3.1 Frontispiece of sighting telescope

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The erecting lens serves to reverse the alreadyinvevted real image formed by the objective lens,so that the final image seen by the observer isan erect one.

The eyepiece provides the chief magnification ofthe system and also serves to form a virtual ima­ge of the crosslines and superimposed target at asuitable distance from the eye for easy viewing.

The optical micrometer is a glass block with ac­curately parallel faces, which is mechanicallylinked to the micrometer drums A light raypassing through the micrometer block when it isnormal to the ray is not affected, but if the blockis inclined the emerging ray is still parallelto the line of the incident ray but is displacedfrom it. The pivoting axes of the micrometerblock are at right angles, so the horizontaland vertical movements of the image are alsoat right angles.

The micrometer block is protected by a coverglass, the inside face of which carries the tar­get pattern used in auto-reflection.

The graduated focusing knob varies the positionof a tube which carries the focusing lens enabl­ing targets to be focused from zero to infinity.

Specification of sighting telescope

Magnification: x 34 at infinity focus (stan­dard eyepiece). The variation of magnificationis given in chart I of the annex.

Focusing: range zero to infinity.

Accuracy of focus scale ± 10% of marked value

Microme~er: range! 1.2 mmGraduat10ns 0,02 mm apartAccuracy 0.003 mm + ~~ ot displacement-axesof micrometer parallel to their respectivecrosslines to within 20 minutes. A click­stop indicates zero reading. The micrometercan be locked at any setting or locked to li­mit the range over which they can be moved.

Cover glass target is concentric with tube towithin 0.025 mm.

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Crosslines are at right angles to each otberwithin 5 minutes.

Field of view for distances up to 3 m' is gi­ven in table 11 in tbe annex. For longer dis­tances it is sbown in tbe chart 11 of the an­nex.

Locating tube outside diameter 57,1~7 -57,145 mmCylindrical within 0,005 mm.

Tube lengtb nominal 254 mm.Overall lengtb with straigbt-througb eye-piece448 mm nominal.Weigbt 4.5 kg approx.

+Accuracy of reading - 0.05 mm at 30 m andproportionally for longer and sborter dis­tances down to 3 m. Below tbis distance tbe

errors are less tban the precision witb wbicbthe micrometer can be read.

3.2. Equipment for sighting telescope

The eyepiece bas a magnification of x 34.It is adjustable for focus and is scaled indioptres.

LOCKING RINGFOR RIGHT ANGLEEYEPIECEADAPTER

Fig. 3.2 Rigbt-angleadapter

Tbe eyepiece can be re­moved from tbe telescopa'~y unscrewing it. Tofacilitate using tbe te­lescope, a rigbt-angleeyepiece adapter (fig.3.2.) is available. Tofit tbis, unscrew the eye­piece from tbe telescopeand screw it into tbe adap­ter. Unscrew tbe straigbteyepiece adapter and tbensecure tbe rigbt-angle adap­ter in its place by meansof tbe locking ring, sett­ing the eyepiece at a con­venient angle for viewing.

The lampbouse for auto-reflection and auto-col­limation is inserted into the telescope and il­luminates the crosslines and cover-glass target.The power supply comes from a 4-volt transformerwhich goes witb it.

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The typical way for use is shown in 'fig. 3.3which gives the scbematic diagram of a auto­reflection setup.

LAMP

CONDENSERLENS

COVERGLASSTARGET

MIRROR

/CROSSLlNES

---~__~J-lI--~-----=~-=7...........:.:.:.:.:.

,';'.,;,:,;,;,;,;,;,;"

IMAGE OFTARGET

MIRROR

Fig. 3.3 Scbematic diagram sbowing Telescope Lampbouseused for auto-reflection.

Tbe lampbouse comprises a source of illuminationwitb screw adjustments for focusing and centeringtbe lamp filament (see maintenance instructions),and a partially-reflecting mirror. A green fil­ter carried on a cross-slide can be brougbt intouse and it is unwise to look tbrougb tbe eye­piece unless tbe filter is in position.

Tbe lJocke~ for tbe lampbouse is diametricallyopposite the focusing knob of tbe telescopeand is normally eQuipped witb an adapter sleeve.

When tbe lampbouse is not installed tbe bole intbe sleeve sbould be closed by tbe cover retainedin tbe telescope by a ball catcb.

To insert tbe lampbouseinto tbe telescope remo-ve tbe protective sleevecovering the mirror andlocate tbe screw bead ontbe mirror stem in tbeslot in tbe adapter sleeve(Fig. 3.4). Pusb tbelampbouse inwards untiltbe screw bead enters aspiral slot tben turn clock­wise until it is beldby tbe ball catch.

Fig. 3.4 Telescope Lampbouse

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The glass reflector is extremely thin and shouldnever be touched. If cleaning is reQuired, wipevery carefully with a lint-free cloth.

The collimator

It is shown in fig. 3.5 and a detailed descrip­tion can be found in chapter 2.3. A buble le­

vel is included to assistsetting the target paral­lel to a crossline.

Specification of collimator

Lamp: 12 V from existingtransformerjoutside diameterof tube 57,137-57,145 mm.Optical axis pl~allel to out­side tube within 3 arcsec.Target concentric with circum­ference of tube to within0.008 mm.

Focal length 21.5 cmWeight 3.15 kg.Overall length: 31.5 cm

Fig. 3.5 Collimator

For replacement of lamp see maintenanoe instructions.

Pentaprism

It consists of the optical sQuare and an adaptor(Fig. 3.6) which permits to fit the unit to thetelescope or to a separate tube for independantinstallation.

TELESCOPETUBE

SPHERE

\I~

4 in -V 90· Line of Sight

~ L.O.S. through "rism

90·

I

- -\- - -

- ~-

TELESCOPEL.O.S. ADAPTER

Fig. 3.6 Four-inch Offset Optical SQuare.

Wedge

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Tbe combination - bere called ~entaprism - al­lows tbe ri§bt-angle line of s1gbt to be sweptthrough 360 clear of obstruction.

Tbe right angle line of sight offset from cen­ter of sphere is 4.00 inches ± 0.001.

Accuracy of 900 angle ± arcsec i.e. 0.005 mm permetre.

The stride level

It is a bubbletelescope tube

",;::"-3.7 Stride Level

level whicb is mounted on theastride the mounting sphere

(fig. 3.7). The construc­tion of the level and theoptical arrangements forreading it permit tbe teles­cope tube to be senlhorizon­tal to within 2 seconds.To obtain this accuracy twoconditions must be satisfied;the vial must be both paral­lel to and vertically abo­ve the axis of the telescope.

The vial is illuminatedthrough the windows at theside of the level and theends of the bubble are vie­wed through the prismaticsystem at the top. If thetelescope is almost level,

half of each end of the bubble will be seenas in (a) or Cb) of figure 3.8. When thetelescope is perfectly level, tbe two imagescoincide as at Cc). If the images are notsYmmetrical about the center line as in (d),the vial is not vertical over the telescopeaxis.

To check and adjust the vial see maintenanceinstructions.

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a b c d e f

Fi~. 3.8 Views of Stride Level bubble(a and (b) Bubble not in coincidence(c)Condition of coincidence(d Vial not vertically over Telescope (e) and (f) Vial not

parallel to Telescope axis.

Mountings

A bore fixture is available which permits tomount tbe telescope concentric with the axisof a bore (fig. 3.9).

To mount the fixture in~ bore or on a surfacean adapter is reQuired. Details for a suita­ble plate are given in fig. 3.10.

The bore fixture is eQuipped with an adjust­ing bracket holding two perpendicular adjust­ing screws and a clamp. The clamp is spring­loaded and is arranged to hold the telescopefirmly on the adjusting pads. It is, however,not strong enough to take the weight of thetelescope so that it has to be pressed intothe pads if one works in odd positions.

Fig. 3.9 Telescope in Bore Fixture

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Vertical line ofBore Fixture

I

H in clearance ortapped'" in B.S,F.

Ffdl~

I *L '"'';.~''' '"J I*C To ,," bo<'=Jt4----To suit method of fixing ------.l

• Concentric with each other

Fig. ;.10 Adapter plate for Bore Fixture

Besides the bore fixture a clamping flan~is available which does not permit any ad ust­ment but is convenient when installing for ins­tance the collimator.

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3.3. One-second theodolite

The instrument is shown in figures 3.11 and 3.12.It is composed of four parts.:

- The tribacb is the base of the instrument. Itbas three footscrews (3), used for setting tbestanding axis vertical, and an optical plummet(4) for centering over ground points. The basepla~e (1) bas a central tbread. The springplate (2) presses the footscrews into tbe baseplate. Tbe circular level (24) allows approxi­mate levelling and together witb tbe opticalplummet is used for levelling and centeringthe tribabb.

The three studs (28) on the base of the instru-­ment pass through holes in the tribach and, whentbe arrow of the swivel locking knJb (27) pointsdownwards, the studs are engaged and the instru­ment is locked in the tribacb. When the knobis turned so tbat the arrow points upwards theinstrument can be lifted out of or placed intbe tribach.

- The lower part contains the cylindrical stand­ing axis system and the horizontal axis. Theaxis sleeve is connected to the centering flangeand studs (28) which fit into the tribacb

The axis stem rotates inside the sl~eve. Forsetting the circle, the horizontal circle carriercan be rotated around the axis sleeve by turningthe circle drive knob (37) which is protectedagainst unintentional use by a cover (38). Amirror (6) is opened for illumination of the ho­rizontal circle and can be replaced by a plug-in lamp.

Left of the mirror is a socket, the input pointfor the internal wiring of the instrument, towbicb a battery box (see eQuipment) can be con­nected for illuminating the circles and reticle.

The upper rotable part of tbe instrument iscalled the alidade. Its main parts are the stan­dards, the vertical circle (13), the tiltingaxis with the telescope, the circle readingoptics, the plate level (22) for setting thestanding axis vertical and the index level.By tightening the horizontal (29) and verti-c~l (11) clamps, the instrument can be clampedw~th the telescope pointing in the reQuired

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direction and the horizontal (23) and vertical(9) drives are used for fine pointing the te­lescope to a target.

One standard holds the vertical circle (13) andits index level, which is centered by turning.the index level setting screw (30) until theends of the split bubble are seen in coinciden­ce in the prism (10). Coincidence indicatesthat the reading system for the vertical sys­tem is plumb. An illuminated mirror (12) whichcan be replaced by a plug-in lamp, is locatedon the outside of the vertical circle housing.

The other standard holds the micrometer knob(16) which is turned to set the images of thediametrically opposed circle graduations incoincidence, and the selector knob (21) forselecting which circle is to be read in theeyepiece (19) of the reading microscope.

The telescope is short and transits at bothends. The eyepiece (20) is rotated for fo­cusing the reticle and has a dioptric scaleto allow immediate setting to suit an obser­ver's eyesight. A bayonet ring (33) holdsthe eyepiece in position. After a slightleft turn of the ring the eyepiece can bereplaced by a diagonal eyepiece, autocolli­mation eyepiece or eyepiece lamp.

The telescope is focused by turning the slee­ve (17), which has engraved arrows to indicatethe turning direction to infinity. When usingelectric illumination eQuipment for sight work,the knob (15) is turned so that light from thevertical circle lamp is reflected off a mi­rror inside the telescope towards the reti­cle. The brightness of the field of viewillumination is varied according to the po­sition of the knob. Immediately beside thetelescope eyepiece is the reading microscopeeyepiece (19) which is turned for focusingthe circle and micrometer images.

For more detailed instructions for use seethe booklet of WILD T2E Universal Theodolite.

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Specification of theodolite

90 mm

70 mm

1 arc sec

20 arc sec

arc sec

20 arc min

x 2840 mm29 m2,2m100

o

8 arc min3600

diam. of

- Magnification- Clear objective aperture- Field of view at 1000 m- Minimum focusing distance- Multiplication constant- Additive constant- Plate level sensitivity

per 2 mm run- Index level sensitivity

per 2 mm run 30- Circular bubble sensitivity

per 2 mm run- Circle glass- Horizontal circle

graduations- Vertical circle diam. of

graduations- Graduation interval of

circles- Smallest scale interval of

opt. micrometer

3.4 Eauipment of theodolite

- The auto-collimation eyepiece as shown in fig.3.13 is inserted in its place after having tur­ned the bayonet ring of the standard eyepieceslightly to the left and having removed the eye­piece. Care has to be taken that the smallest pinof the auto-collimation eyepiece engages exactlyin the corresponding notch in the eyepiece mount.Between the eyepiece lenses and the reticle the­re is a beam splitter aligned at an angle of 450

to the line of sight. A plug-in lamp which hasto be connected to the batte­ry box is inserted intothe auto-collimation eye­piece from below.

The image of the crossli­nes reflected back into thetelescope from the mirrortarget is only visible ifthe telescope is focusedto infinity.

Fig. 3.13 AutocollimationEyepiece GOA 2

The 1,rallelis f tted to

plate micrometer (fig. 3.14)the front of the telescope.

The mounting has twonotches , at 900 toeach, by means of whichthe micrometer is positio-ned to measure displacementsin either the horizontal orthe vertical plane. The rangeis 5 mm on either side of thetelescope's line of sight.Direct reading is possibleto 0.2 mm and estimationgoes down to 0.05 mm.

Fig. 3.14 Wild T2 with ParallelPlate Micrometer GPM2and counterweight.

- The zenithing around

eye1iece (fig. 3.15) permits read­zen tb position. The reading eye­

piece is unscrewed and thediagonal zenith eyepieceis slipped into the tubeand clamped by means ofa small lever. After transi­tting the diagonal eyepie-ce gan be rotated through180 •

Fig. 3.15 Diagonal Eyepieces orsighting to the zenith.

An electric illumination set (fig. 3.16)consists of a metal battery box with accesso­ries. The box holds six dry cells. The three

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Fig. 17 Battery Box

45 Switch and rheostat knobfor regulating instrument

:~~::ti~:~~ illumination46 Handlamp with cable48 i~••~- 49 47 3 batteries in the circuit

48 3 spare batteries47 49 Spare bulbs

""--50 50 Push button for sliding co­ver protecting the sockets

46 51 51 Socket for handlamp, auto-52 collimation eyepiece or

eyepiece lamp52 Socket for instrument

ilIUl1linntion45---

Fig. 3.16 Battery Box

inner ones are connectedin series with the switchand plug sockets. The threeouter ones are spares. Al­so contained in the box areconnection cable, four reser­ve bulbs and a handlamp. Theswitch serves as a variablerheostat for regulating thebrightness of the bulbs.

The sockets of the batterybox are protected by a slid­ing cover. The outer socketis controlled by the rheostat.

ThA heaVY duty :'stand_ shc...wn

in fig. 3.17 takes thetheodolite on a table withcrossed slides. The stro­ke of the slides is • 50mm. The table can be lif­ted from 1.4 m to about2.8 m height.

Fig. 3.17 Heavy duty stand

3.5. Targets and target holders

All targets available have an outer diameter of2 1/4 Inch or 57,132-57,148 mm. The target pat­tern is either a crossline framed in a steel ringor a pattern as shown in fig. 3.18 with ,etric

Fig. 3.18 StandardPattern.

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scale. The latter patternis onl~ used for direct view­ing because the parallelismof the glass plate whichholds the pattern is 20 arcsec. Same targets are avai­lable with mirror surface.They have to be located a­gainst the front face.

The circular target patternsare concentric to their outerdiameter within 0.0064 mm.Their thicknes is 0.5 inch

Circular or 12,45-12,95 mm.

Fig. 3.19 Spider Fixture

- The target holders exist in different forms andcover a big variety of utilisation cases. Main­

ly for the cross-lines tar­gets and for installationin big holes two spide~.

fixtures are available si­milar to fig. 3.19. Theyare extendable from a dia­meter of 16 inch to 681/2inch (405 to 1680 mm). Thespider can be eQuipped witha rotating arm and micro­meter clock for centering.

Several mounting spheres(fig. 3.20) can take alltargets mentioned above.They can be eQuipped withtarget illuminators (fig.3.21) with 220 V lamps

Fig. 3.20 Mounting Sphere showing (left to right): colletclamp ring, collet, body, shoulder ring.

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Fig. 3.21 Target Illuminator

and fixed to flange cupsas shown in fig. 3.22.

A target frame (fig. 3.23)with magnetic feet can al­so be eQuipped with all tar­gets abd the illuminator,whilst the ad~ustable tar­~et holder (f1g. 3.24) can

e tilted about two perpen­dicular axes but cannottake the illumination•. Itis located with a 3.75 inch(95,25 mm) spigot in thecorresponding structure.

Fig. 3.22 Sphere Clamp holding Sphere onto Flange Cup.

Fig. 3.23 Magnetic TargetFrame

Fig. 3.24 Adjustable MirrorTarget Holder

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4. Alignment procedures

In this chapter the fundamental alignment ... proceduresand possibilit~s are described which are necessaryto set the telescope structure according to the opticalreCJuirements.

4.1. Instrument pole

The pedestal of the telescope rests on three feet­one at tbe nortb end and two in tbe south. Allthree feet are adjustable in height. But it isonly tbe north foot which is used for alignmentof the telescope pole in height.

For displacement work the two safety screws onboth sides of the pedestal's north end have tobe loosened and with two 100 ton hydraulic jacksone has to lift the pedestal slightly by placingthe jacks under the structure close to the safetyscrews.

According to the calcula­ted value one has to chan­ge the length of the footby turning the screw whichis accessable inside thebig central tube of thepedestal.

The screw is secured againstrotation by a flange cup

1:--., (see fig. 4.1) and has ahexagon head of 46 .m widtb.One turn corresponds to 6mm displacement. Afteradjustment tbe safety screwshave to be retigbtened.

..

I ~--I If ••,

ll-1~ I (~

I ~ I I,

~,

- I ~

I i, .i I "'"

,- 1\ l f ~,

t:'-r . ! ,

r ,I

r

I

i .. I~

!

l~,--_.

I ( I. , .- -

. -~

I IFig. 4.1 Top end of north foot

Whilst the north foot permits only displacements along itsaxis and rotations about it tbe two south feet also can bemoved sideways. A number of push-pull screws underneath thepedestal and located half-way between the south feet areforeseen for these adjustments of the instrument pole inazimuth.

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Attention! do not loosen the push-pull screws forbig amounts because the north feet have a built inspacer in unstable position to permit the lateraldisplacement. Ensure that the telescope pedestalfollows when you loosen one side of the screw set.Otberwise you have to push from the other side.

Tbe pedestal should not be moved for more than 5mm in botb directions. (Cbeck on push-pull system!).

4.2 Perpendicularity of alpha and delta axis

The first operation is to install targets in tbecenters of the two axes.

For declinationone can use the spider fixtures (fig.3.19) which are placed in the holes bidden behind acover on the inner diameter of the center pieces.

The sighting telescope is installed with the borefixture and a triangular support on the westof tbe telescope part as shown in fig. 4.2.

To center the targetsone has to follow the instruc­tions of chapter 2.5.

Triangular support

x-v Table

Sighting telescope

Fig. 4.2

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The targets of the polar axis are already placedon the cross-beam and on the northend. In themirror 5 point the theodolite has to be installedusing the heavy duty stand. The theodolite shouldbe eQuipped with the standard eyepiece and theparallel plate micrometer.

To center the targets one has to follow the instruc­tions of chapter 2.5.

P£N1AMISN

DI3TAf'lC£ TUBE:

The 3.6 m telescope tubehas now to be brought intopole position. By placing

align the two instruments(the sighting telescopeand the theodolite) totheir two correspondingtargets. Thus one hasinstalled a right angleline of sight passingthrough the center of al­pha and delta axis.

To check this angle thebase of mirror 3 has tobe demounted and replacedby the pentaprism supportshown in fig. 4.3.

The pentaprism is fixedto the support as indica­ted in fig. 4.4. This con­figuration permits anadjustment in height bysimply displacing the pen­taprism adapter up and down.

- a fil€ rotation about thereticle axis by means ofthe target screw.

- A tilt using the screwsof the adjustable targetholder.

Looking through the sight­ing telescope one has toadjust the height of thepentaprism to be more orless centered to the exitaperture.

AOAPTOq._--

It is now necessary to

4.3 Pentaprism support

--,-----'-----,.----l..l.!...l..---.-- , _

.'

Fig. 4.4 Pentaprism mouting

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a small but good ~uality mirror onto tbe straigbttbrougb exit of the pentaprism and e~uipping tbetbeodolite for auto-collimation one can align tbepentaprism to be perpendicular to tbe polar axisusing tbe tilt screws of tbe adjustable targetbolder.

Looking tbrougb the rigbt angle exit the pentaprismis now rotated rougbly to set tbe front target oftbe sigbting telescope onto tbe borizontal line oftbe crosslines of tbe tbeodolite. For centeringtbe target in tbe borizontal direction one bas tocbange tbe beigbt of tbe pentaprism (lifting tbepentaprism means tbe target image moves to tberigbt).

Witb a transparent scale placed on tbe rigbt angleexit of tbe pentaprism one defines the distancebetween alpha and delta axis by looking tbrougb tbetwo sighting instruments. Tbe pentaprism bas tbento be rotated again to show the target of tbe sigbt­ing telescope displaced downwards in the eyepieceof tbe tbeodolite. Tbe displacement value correspond­ing to tbe distance or tbe axes can be read on amillimeter scale placed in front of tbe sigbtingtelescope.

After an additional cbeck of tbe position of tbepentaprism tbrough tbe above mentioned auto-colli­mation procedure one bas to e~uip tbe sigbting te­lescope with tbe lampbouse and focus it to infi­nity thus converting it into a collimator.

Focusing tbe tbeodolite to infinity and using itsstandard eyepiece tbe sigbting telescope crosslineswill appear on tbe vertical line of tbe tbeodolitecrosslines under the condition tbat alpba and deltaaxes are pe~~ndicular. Tbe tolerance for lateraldeviation is - 6 mm wbich corresponds to ±'1 arc minwitb a distance between tbeodolite and sigbting te­lescope-collimator of about 20 meters.

If tbe measured value is bigber one bas to tilt tbedelta axis by adjusting tbe hydrostatic pads. Fortbis work see maintenance manual 1 and 7.

4.3. Perpendicularity of delta-and tube axis

Tb~ tube axis is defined only by tbe optics of tbe3.6 m telescope and bas tberefore no real mecbanicalcenter. Special procedures are necessary for settingtbe optical axis perpendicular to tbe delta axis.

- 24 -

It would go too far to indicate these procedures with­in t"lis manual. A separate manual on the alignment ofthe optics will give the details.

4.4. Mirror and top units

The following chapter explains the alignment facilitieswhich exist to displace or rotate the five mirrorswhich form the optics of the 3.6 m telescope.

But first a general remark: all mirrors cannot bedisplaced in one way or other inside their cells. Thegeometry of the configuration mirror-cell is thereforeinvariable.

All alignment facilities are installed in the mecha­nical part between the cell and the fixation to thetelescope.

The main mirror cell can be tilted through about ±3 arc min. This is done by turning the fixation nutsof the six flexion bars on top of the center section.

According to the tilt direction one has either to un-do 2 nuts and to lift the others 2 on opposite sideor three nuts on one side down and three nuts up. Thedisplacement has to be calculated beforehand and checkedby micrometer clocks.

~,~:/~--G), ,

jf-4N~1

Fig. 4.5 Nut system of FlexionBars.

To turn the nuts one has toundo first the 4 screws (1)in fig. 4.5 (left side) tillthe ring (2) is free. By'turning the counter-nut (3)tbrough 450 one can turndown the 4 screws (1) againand thus lift the bolt (4)of the flexion bar. (fig.4.5 right side).

According to the directionone has to mount or to des­cend the nut (5) and to loosenthe screws (1) and afterreturning them through 450

they have to be screwed intothe center section to blockthe counter-nut.

Attention I displacement steps should be very small, becausethe flexion bars are rigidly fixed to the main cell. Displace­ments of more than 0.3 mm on one bar could cause serious defor­mation••

- 25 -

There is no possibility given to displace the mainmirror cell laterally.

- The top units however have been e~uipped with thisfacility. The spider fixftion in the top-ring permitslateral displacements of ~ 5 mm. According to the di­rection one has to release or tighten two times twoopposite screws (1) ae shown in fig. 4.6. These screwsare mounted under preload. It is therefore necessaryto tighten the nuts (2) through the same angle as theopposite ones were loosened.

The cells of mirrors 3and 4 are also e~uippedwith motorised three pointfixations to the telesco­pe structure. Longitu­dinal displacements andtilting is possible.

secondary mirror cells (Coude and Cassegrain)fixed to the top-units through a drive system

which allows longitudinaldisplacement (focussing)and tilting (collimation).As these movements are moto­rised no further descriptionis necessary.

Fig. 4.6 Alignment screws on topring

A slight tilt of the top unit is also possible byturning the screws (1) in fig. 4.7 which are fixedto the spider piece (3) in fig. 4.6 and 4.7.

Theare

~I

I

L.~...............~ L1'£::==::z=:E::2Z

Fig. 4.7 Tilt screws on top-ring

- 26 -

The mirror configuration in itself works likean alt-az muth mounting and permits correctionsin tilt and rotation about the vertical axis.

5. Maintenance instructions

5.1. Change and adjust lamp of telescope lamp-house

It is essential that only the correct lamp (code613/48 Rank Precision Industries Ltd. Leicester,Englani) should be used with the lamphouse. Toreplace the lamp, remove the cover by withdraw­ing the four radial screws at least 1/8 inch andthen unscrew the lampbolder assembly. If the ra­dial screws are not witbdrawn sufficiently, theywill foul tbe lamp wben the lampholder is removedor inserted.

Note that the lampholder is insulated from itsmounting and is supplied with current via theradial screws. Therefore, the lamp will not lightuntil one of tbe radial screws bas been screwedup to make contact.

After replacement of the lamp reassemble the coverand insert the lampbouse into the telescope. Ope­rate tbe slide to remove the green filter from tbelight path. Place a piece of white card about 40cm in front of the telescope and by turning thefocussing knob focus an image of the crosslinesonto the card.

Next rotate the knurled ring on the lampThouse tobring tbe lamp filament into sbarp focus and usetbe focus adjusting screws to center the image ofthe lamp on tbe crosslines. Turn the knurled ringto tbe stop position to diffuse tbe image of thefilaments and the lamp is now set to give maximumillumination.

5.2. Replacement of Collimator lamp

To replace the lamp,undo the two knurled screwsin the lamphouse, at the same time bolding the capdown against the spring pressure. Remove the cap,replace tbe lamp and re-assemble, making sure thatthe pin is located in the hole in the cap. No fo­cussing is necessary.

- 27 -

Replacement lamp 12 V, 4 Watt (Code 104/122Rank Precision Industries Ltd., Leicester,England).

5.3. To Check and Adjust the Vial of the Stride Level

The accuracy of the vial can be checked by settingthe telescope, eQuipped with the level, horizontaland Unclamping the level and reversing it end forend without disturbing the position of the telesco­pe. The images should again be coincident. Ifnot, the error can be corrected as follows:

Take up half the error by means of the telescopeheight adjustment screw on the adjusting bracket.Take up the remainder by turnin~ the capstan under­neath the level, using a cranked tommy bar.Reverse the level and re-check; if necessary elimi­nate any residual error in the same way.

If the two images of the bubble do not form a com­pletely circular curve when they are in coinciden~

ce, the vial is skewed in the mount and its axisis not parallel to the telescope axis. To correctthis, adjust the upper one of the two screws bythe side of the window, below the circular level.Do not attempt to adjust the lower screw.

ANN E X

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Angle mm per l1etre

1 sec 0,0052 sec 0,013 sec 0,0154 sec 0,025 sec 0,0256 sec 0,037 sec 0,0358 sec 0,049 sec 0,045

10 sec 0,0520 sec 0,1030 sec 0,1540 sec 0,2050 sec 0,25

1 min 0,302 min 0,603 min 0,904 min 1,205 min 1,506 min 1,807 min 2,108 min 2,409 min 2,70

10 min 3,030 min 9,0

1 deg 17,5

Table I Angles expressed as gradients

Jf~eld ofDistance ViewMetres ~~~-B~lea

mm

0,3 180,6 250,9 301,2 381,5 431,8 482,1 532,4 612,7 693,0 74

Table 11 Field of view of sighting telescope fordistances up to 3 m.

- 30- -

X50

X40c0 --- --

... - X30o 0:i v With standard ~ypi~c~01;: X20C "-c{ c 112/554C7l

0 X 10~

10 20 30 40 50 60 70 80 90 100 het0

3 6 9 12 15 18 21 24 27 30 mftr~s

Distance Of Obj~ct From TlZI f scop~.

Chart I Overall magnification of eighting telescope

Distance From Telescope In Metres

3 9 12 15 18 21 24 27 30

o

•..20>

o:2..u:

50

60

40 ~..~

:!c:30 ~

100908070605040302010

-- f----- t---- --- --t---- .--- f----- t---~-- - - ---

/'V

- -- -- --- -- - --- With Standard Eyepiece V-- - With High Magnification Eyepiece V

V..... '

V ..-'

/' .... '

V ..... './ .... '

V .... ........

V ,-I V , ....

,-

./~ "

/~....

- ,

V' II

~~

,

4

o

2

\8

16

24

22

20

VIl! 14

~oS 12

~ 10">o 8

~. 6u:

Distance From rtlntOpf \n Feet

Chart II Field of vie~of sighting telescope tor distancesover 3 meters.